1. Field of the Invention
The present invention relates to an automotive air conditioner capable of ensuring oil return performance even at a light load of cooling, and more particularly to an automotive air conditioner comprising an engine-driven refrigerant compressor which carries out capacity-variable control according to various air-conditioning environmental factors.
2. Description of Related Art
A conventional automotive air conditioner disclosed in Japanese Unexamined Patent Publication No. 147260/1989, for example, is provided with a refrigerating cycle system comprising a refrigerant compressor, which performs capacity-variable control in response to a control signal output according to result of comparison between a target post-evaporation temperature and an actual post-evaporation temperature detected by a post-evaporation temperature sensor. In this conventional system, when the actual post-evaporation temperature approaches the target post-evaporation temperature, i.e., when a cooling load is reduced to decrease a discharge capacity of the refrigerant compressor, a periodic switchover operation is performed to increase the discharge capacity of the refrigerant compressor to enhance returning oil to the refrigerant compressor.
In this conventional arrangement, in which the oil return performance under a decreased cooling load condition is ensured by increasing the discharge capacity of the refrigerant compressor periodically, significant periodic variation in torque on the refrigerant compressor occurs when the discharge capacity thereof is periodically changed from a low level to a high level. In an engine that drives the refrigerant compressor by means of a belt, a rotating speed thereof varies significantly in cycles, causing degradation in motor power performance, such as accelerating performance and climbing performance, and automobile drivability.